The present invention relates to the preparation of curable pellets of polyethylene or copolymers of polyethylene.
In order to produce extruded articles from curable pellets of polyethylene or its copolymers a crosslinking agent of curing agent must be uniformly dispersed throughout the polymer. Heretofore, curable pellets of polyethylene and copolymers of polyethylene have been prepared by methods: ( 1) in which polyethylene or copolymers thereof and a curing agent are mixed on a two-roll mill and the resulting band pelletized using a pellitizer; (2) in which the polyethylene or its copolymers and a curing agent are first premixed in a mixer such as a ribbon blender or vortex mixer, then fused and mixed in a twin-screw continuous mixer and subsequently pelletized; (3) in which polyethylene or copolymers thereof and a curing agent are mixed using a Banbury mixer and thereafter calendered using a two-roll mill and thereafter the mixture is pelletized; or (4) in which the polyethylene or copolymers thereof and inert fillers and other additives are fused and mixed in a twin-screw continuous mixer or Banbury mixer and the mixture is thereafter pelletized and the curing agent is subsequently added at a later time in a high intensity mixer by stirring curing agent and pellets at a high speed until the curing agent is evenly dispersed on the pellets and absorbed therein.
The above methods have shortcomings in that the pellets produced are likely to become contaminated during the milling and mixing state thereby causing the extruded articles produced therefrom to have impaired dielectric properties. Moreover, the cost of the equipment used is high and the production rates are low.